Requires Mg2+. Two isozymes with this activity were isolated from the bacterium Streptomyces sp. SANK 60404. The enzyme encoded by the DtcycA gene also produces cembrene C (see EC 4.2.3.148, cembrene C synthase), while the enzyme encoded by the DtcycB gene also produces (R)-cembrene A and (1S,4E,8E,12E)-2,2,5,9,13-pentamethylcyclopentadeca-4,8,12-trien-1-ol (see EC 4.2.3.150, cembrene A synthase, and EC 4.2.3.151, pentamethylcyclopentadecatrienol synthase).